1. Field of the Invention
The present invention concerns tooling for abrasive belt machining of cylindrical bearing surfaces on parts, especially journals and crankpins of crankshafts, allowing monitoring of the bearing surface diameter.
2. Description of the Prior Art
The prior art abrasive belt machines described in patent application EP-A-0 366 506 include, for each bearing surface to be machined on a part, a pivoting and vertically mobile arm and three abrasive belt application shoes of which a first is mounted in a top median position on the arm and the other two are mounted in bottom lateral positions on two jaws articulated to the arm and coupled together so that they can be clamped together so that when clamped against the bearing surface to be machined the three shoes are substantially at the three corners of an equilateral triangle.
On these prior art machines, the abrasive belt application shoes have a circular arc shape application surface subtending a relatively small angle, usually less than 30.degree.. These tools produce a good surface state of the bearing surfaces.
Stones have been used for honing cylindrical bearing surfaces on parts, the stones having a circular arc shape surface in contact with the bearing surface to be machined and subtending an angle of up to 60.degree.. However, in use these stones are subject to asymmetrical wear with the result that in practice they apply pressure to (and therefore exert their machining effect on) the bearing surface to be machined over an angle much less than 60.degree..
On the other hand, honing and abrasive belt machines using stones or shoes subtending angles of more than 30.degree. are better able to compensate defects of shape (ovalization, out-of-round, etc) and defects of straightness of parts, because of their enveloping shape.
Some abrasive belt machines have tools in contact with each cylindrical bearing surface to be machined which include two opposed abrasive belt application shoes disposed on two jaws of a clamp and which can each have a circular arc shape application surface subtending an angle of almost 180.degree.. The drawback of these prior art shoes used in pairs is imperfect distribution of the application pressure. The pressure is inevitably concentrated in the median part of the length of the circular arc shaped surface of each of the two opposed shoes.
On abrasive belt machines with two opposed application shoes, one of the two shoes has been associated with a gauge mounted on one of the jaws and including two opposed and aligned sensors to measure the diameter of the bearing surface during machining and optionally to stop machining when the diameter reaches a predetermined value.
We do not know of any use of a diameter monitoring device on abrasive belt tooling including three enveloping shoes disposed in a triangle, the first on an arm and the other two on two jaws articulated to said arm.
The present invention concerns tooling for application of an abrasive belt to cylindrical bearing surfaces to be machined on parts, especially journals and crankpins of crankshafts, allowing monitoring of the diameter of the bearing surfaces, the tooling including enveloping shoes able to meet severe requirements in respect of the absence of shape defects, the straightness and the precision of the bearing surfaces.